In conventional offset printing machine, which require several fundamental steps such as inking, dampening, paper feeding, printing, and blanket cleaning, various inventions and modifications have been made regarding mechanisms for controlling the aforementioned steps. Existing mechanisms before the present invention for controlling offset printing machines, especially in small offset printing machines suitable for business office work, are mechanically too complicated and at the same time, are cumbersome from an operator's standpoint. For example, in the mechanism shown in the U.S. Pat. No. 3,601,045, the blanket cleaning position of the control shaft is located between the original neutral position and the printing position. If there were no second neutral position, in case of any printing trouble such as paper jam, the control shaft had to be quickly shifted to the original neutral position through the blanket cleaning position, which means that the blanket surface would momentarily touch the blanket cleaning roller resulting unintentional inking on the surface of a master plate on resumption of printing. Accordingly, a second neutral position is provided before the blanket cleaning position so that in case of any printing trouble such as paper jam, the control shaft can be quickly shifted to the second neutral position without the blanket surface touching the blanket cleaning roller. Because of the existence of the second neutral position, the mechanism becomes inevitably complicated. Another example of a recent invention of control mechanism can be seen in the U.S. Pat. No. 3,731,367 and 3,731,624. In this mechanism, the blanket cleaning position of the control shaft is located beyond the original neutral position looking from the printing position of the control shaft. Because of the use of an operation lever that can not rotate 360 degree, it would be almost impossible to convert the mechanism so as to automatically clean the blanket after a pre-set number of sheets are printed.
The present invention provides a simplified control mechanism for easier operation.